NEW YORK (Reuters) -- U.S. President George W. Bush has deflected Israel's secret request last year for bunker-busting bombs it wanted for an attack on Iran's main nuclear complex, saying he had authorized covert action to sabotage Tehran's suspected atomic weapons development, "The New York Times" said.

Citing U.S. and foreign officials, the "Times" reported on January 10 that the White House was unable to determine whether Israel had decided to carry out the strike before Washington objected or whether Prime Minister Ehud Olmert was trying to get Bush to act more decisively before he leaves office this month.

Israeli government officials declined comment on the report.

A U.S. official told Reuters in September that the Pentagon had refused an Israeli request for unspecified "offensive" items that could be used on Iran. To reassure the Israelis, Washington instead gave them advanced radars for spotting missile launches.

Details of the expanded U.S. covert program and the Bush administration's efforts to talk Israel out of attacking Iran emerged from 15 months of interviews with current and former U.S. officials, international nuclear inspectors, outside experts and European and Israeli officials, the "Times" said.

None of those interviewed would speak on the record, the paper said, adding it omitted many details of the covert efforts from its report at the request of senior U.S. intelligence and administration officials.

It said the interviews also suggested "that while Mr. Bush was extensively briefed on options for an overt American attack on Iran's facilities, he never instructed the Pentagon to move beyond contingency planning, even during the final year of his presidency, contrary to what some critics have suggested."

But aware that financial sanctions against Iran were inadequate, Bush turned to the CIA, according to people involved in the covert program, authorizing a broader effort aimed at Iran's industrial infrastructure supporting its nuclear programs, the "Times" said.

While the paper said details were closely held by U.S. officials, it quoted one as saying, "It was not until the last year that they got really imaginative about what one could do to screw up the system."

But the official said "none of these are game-changers" in that the efforts would not necessarily cripple Iran's program.

Flyover Request

Under Bush, whose term ends on January 20 when Barack Obama becomes president, the United States has sought tougher UN sanctions against Iran to halt its nuclear program, which Western states believe is designed for making weapons.

Iran, which has no formal diplomatic relations with the United States and often unleashes virulent rhetoric against Israel, insists its nuclear program is for civilian purposes.

The "Times" said some Bush administration officials remained skeptical of the covert program's chances of success given what one said was Iran's proximity to achieving weapons capacity.

Others held that Israel would not have been dissuaded from attacking if they believed the U.S. effort was unlikely to prove effective, the paper said. Israel backs the U.S.-led diplomatic pressure on Iran but has refused to rule out a military option.

Widely believed to have the only nuclear arsenal in the Middle East, Israel bombed the site of a suspected atomic reactor in Syria in 2007.

In its dealings with Israel, Washington was especially distressed by Israel's request to fly over Iraq to reach Iran's major nuclear complex at Natanz, a request the White House flatly denied, the paper reported.

But the exchanges and tension prompted Washington to step up its intelligence-sharing with Israel, including the new U.S. efforts aimed at sabotaging Iran's nuclear infrastructure.

The "Times" said its interviews indicated Bush was convinced by officials, led by Defense Secretary Robert Gates, that an overt attack on Iran would likely be ineffective, bringing the expulsion of international inspectors and driving Iran's nuclear effort further from view.

"Mr. Bush and his aides also discussed the possibility that an airstrike could ignite a broad Middle East war in which America's 140,000 troops in Iraq would inevitably become involved," the paper said.

Bush instead opted for more intensive covert action, it said, adding that those operations and the issue of whether Israel would agree to anything less than a conventional attack on Iran posed vexing problems for Obama.